1. Field of the Invention
This invention relates to range finders and sights for determining the direction and distance from a viewer to a distant object for use with guns and the like, and more particularly to a sight employing a hologram and means for reconstructing a three-dimensional light line from the hologram so that it is superimposed on a scene viewed through the hologram, to provide information relative to the distance and direction from the viewer, of objects in the scene.
2. Prior Art
Conventional sights for aiming guns, surveying instruments and the like, or range finders for determining the distance from the observer to the object, typically impose close limitations on the position of the viewer's eye relative to the sight. Hairline sights as used on rifles depend for their accuracy on the exact alignment of the observer's eye with the two sight elements. Telescopic sights typically restrict the observer's eye to within an inch or so. Both of these forms of sights severely restrict the field of view about the target making it difficult to locate a target within the sight. Both of these limitations render it difficult to use the sights on moving vehicles or in other situations where the observer is subjected to vibration and impacts.
U.S. Pat. No. 3,633,988 proposes a form of sight which overcomes these limitations by employing a hologram interposed between the observer and the target. The image of a point located at infinity may be reconstructed from the hologram so that the observer views the target object with the image of the point superimposed. By manipulating the hologram and its coherent source to align the point with the target object, the direction to the target may be ascertained. The observer's eye may be moved through the relatively large area which will allow him to observe both the reconstructed point and the target through the hologram plate and the observer's field of view of the target is not in any way artificially restricted.
U.S. Pat. No. 3,737,212 discloses a similar structure employing a hologram which is capable of projecting the image of a point or a reticle on a target viewed through the hologram. Despite these advantages such sights have not gained widespread use because of the necessary compromise that they impose between viewing ease and precision. If the projected point is made large enough for easy viewing it inherently blocks the view of the target and limits the precision with which the point can be aligned on the target. If the point is made smaller, easing these limitations, it becomes difficult to locate on the scene.
While the images of points that are used for aiming with these holographic sights theoretically may be viewed in three dimensions, as a practical matter, their three-dimensional nature is not meaningful since they appear at infinity and any movement of the observer's head relative to the hologram produces very little movement of the point relative to the observed scene.